1. Field of the invention
The present invention relates to a process and an apparatus for nitriding an aluminum-containing substrate.
2. Description of the Related Art
As wirings in the semiconductors and liquid crystal panels become finer, fine workings with dry processings are progressing. With the demand for such fine workings, halogen-based corrosive gases are used as film-forming gases or etching gases for the semiconductors or the like. On the other hand, it is known that aluminum nitride exhibits high corrosion resistance against such halogen-based corrosion gases. Therefore, members having aluminum nitride on their surfaces have been used in semiconductor-producing apparatuses, liquid crystal panel-producing apparatuses and the like. More specifically, there are available powdery aluminum nitride-sintered materials, in which an aluminum nitride film is formed on a substrate by using a vapor deposition technique such as CVD, and materials in which a surface of aluminum is modified and aluminum nitride is formed thereon.
When aluminum contacts air, its surface is oxidized to form a thin oxidized film. Since this oxidized film is an extremely stable passive phase, the surface of aluminum can not be nitrided by a simple nitriding method. Under these circumstances, the following methods have been specially developed to modify the surface of aluminum and form aluminum nitride thereon.
JP-A-60-211061 discloses a method in which after the inner pressure of the chamber is reduced to a given level and hydrogen or the like is introduced thereinto, discharging is conducted to heat the surface of aluminum to a given temperature, further argon gas is introduced and discharging is conducted to activate the surface of aluminum, and the surface of the aluminum is ionically nitrided through introducing nitrogen gas.
JP-A-7-166321 discloses a method in which a nitriding aid made of aluminum powder contacts the surface of aluminum, and aluminum nitride is formed on the surface of aluminum through heating in a nitrogen atoms-containing atmosphere.
However, according to the method described in JP-A-60-211061, since aluminum nitride is formed by using discharging, the entire device is complicated, which raises the costs. Further, it is difficult for this method to nitride members having complicated shapes or large sizes.
Furthermore, according to a method described in JP-A-7-166321, since a nitriding aid is used, voids exist in a resulting surface layer of aluminum nitride so that denseness is not sufficient. For this reason, it is an actual situation that corrosion resistance of the surface against the halogen-based corrosive gas is not sufficient and not practicable.
Moreover, when sintered aluminum nitride is to be used, it is needed to sinter aluminum nitride powder at a high temperature and the sintered body is difficult to be worked, thereby raising the cost. Further, it was extremely difficult to form members having large sizes or complicated shapes. In the case that an aluminum nitride layer is formed by a CVD process, aluminum nitride members having large sizes or complicated shapes are difficult to be formed, and the device and the process are complicated and expensive.
NGK Insulator, Ltd. discloses a technique in Japanese Patent Application No. 11-059011, in which a nitride film is formed on the surface of aluminum by heating the aluminum in the nitrogen atmosphere immediately after heating it in vacuum. However, depending on various conditions such as the shape of a container and the number of times of growing the films, the quality of the nitride film is degraded, or the growing rate of the film is decreased, or, in some cases, the nitride film is extremely difficult to be grown. For this reason, the technique may cause a disadvantageously large fluctuation as a nitride film producing method.
It is an object of the present invention to provide a process for producing a nitride film with a stable quality, when the nitride film is formed on an aluminum-containing substrate.
It is another object of the present invention to reduce a fluctuation in forming the nitride film, when the nitride film is formed on an aluminum-containing substrate.
The present invention relaxes to a process for nitriding a substrate containing at least metallic aluminum. The process includes the steps of heating the substrate in a vacuum of 10xe2x88x923 torrs or less, and heating/nitriding the substrate in an atmosphere containing at least nitrogen continuously during the heating step. A porous body, through which a nitrogen atoms-containing gas can flow, is contacted with the nitrogen atmosphere during the heating/nitriding step.
The present invention also relates to an apparatus for nitriding a substrate containing at least metallic aluminum by the steps of heating a substrate containing at least metallic aluminum in vacuum of 10xe2x88x923 torrs or less, and heating/nitriding the substrate in an atmosphere containing at least nitrogen continuously during the heating step. The apparatus includes a vessel for receiving the substrate arid enclosing the nitrogen-containing atmosphere during the heating/nitriding step, and at least a part of the vessel includes a porous body through which a nitrogen atoms-containing gas can flow.
The present invention also relates to an apparatus for nitriding a substrate containing at least metallic aluminum by the steps of heating a substrate containing at least metallic aluminum in vacuum of 10xe2x88x92""torrs or less, and heating/nitriding the substrate in an atmosphere containing at least nitrogen continuously during the heating step. The apparatus includes a vessel for receiving the substrate and enclosing the nitrogen-containing atmosphere during the heating/nitriding step, a gas-supplying path for supplying at least a nitrogen atoms-containing gas into the vessel and a porous body arranged in the path through which the nitrogen atoms-containing gas can flow.